More than 3 years ago, I designed the CSS Selector Builder. It does not work any more in Firefox because of - among other things - the deep changes in XUL trees. I was very surprised to find it today, under exactly the same name, implemented by CSSEdit since version 2.5 in april 2007, so a bit less than two years after me. Let me quote CSSEditor's blog here:

Selector Builder. Selector what? This is a brand new innovation that should make life much, much easier for anyone starting out with CSS (or teaching it). Define your selectors in plain English, and it generates the necessary code for you.

Speaking of "brand new innovation", the person who sent me this information about CSSEdit asked me "You're listed in the credits I hope?". Hummmmppphhh, to say the least...